Thermal and Electrical Evaluation of SiC GTOs for Pulsed Power Applications

For applications which require high peak current and fast rise time, silicon carbide (SiC) material is ideal because of its ability to tolerate high localized temperatures generated during switching. This research was performed to investigate SiC devices for pulse power applications and to analyze the failure of the devices. Seven 2 mm X 2 mm SiC gate turn-off thyristors (GTOs) manufactured by Cree, Inc., Durham, NC, were evaluated. The devices were tested at single shot and under repetitive stress using a ring-down capacitor discharge circuit. The current pulsewidth was 2 μs with a peak current of 1.4 kA (current density of 94.6 kA/cm²) and a maximum di/dt of 2.36 kA/μs. The maximum power dissipated within the devices was 240 kW. Thermal modeling of these devices was done using ANSYS to analyze the heating and cooling. A two-dimensional model was used that included the device package and bonding materials. The maximum amount of power dissipated was calculated from the 1000-A, 2-μs pulse. No further power input was added to the model and the heat transfer was plotted on an exponential scale. It was found that heat applied to a 2-μm-thick region of the fingers yielded a temperature greater than 800 °C in the device. It took 1.0E^-02s for this heat to dissipate and for the device to return to 23 °C. The minimum and maximum stresses were found to be -2.83E⁺⁰⁹Pa and 4.06E⁺⁰⁸Pa, respectively.